Running V brakes on Ultegra equipped Cross Check

I'm getting my Surly Cross Check soon, I'm looking at brake options. My LBS, who will probably sell & build it, didn't even consider the question, I was talking about Ultegra, so I think they're assumming canti. I'm a fan of v-brakes, from loaded touring in the Loire Valley to this morning's muddy rocky descent in the Dublin Mountains.

I've never used cantis. I haven't read a lot of good about them, and I've seen negative remarks about their stopping power. I'm over 200lbs and will be using the bike for loaded touring, we're talking a total package near the 300lbs mark (I'm not sure which side of it ).

Can cantis do the job for me, or do I need to ask them to swap? Will it cost more?

I've both ridden and worked on tandems that use linear pull brakes and travel Agents for many years. That's what I would recommend.

A decade or so ago we used to worry about the brake cable breaking at the kink that's required by the Travel Agent. That hasn't been a problem probably because the kink itself doesn't move. It's held firmly in the same orientation.

Tektro makes a short arm linear pull brake that's not supposed to need a Travel Agent. I hate them. To make them work you have to set them up so close to the rim that you have to either deflate the tire or readjust the brake cable to remove a wheel.

Like hairlessbill, I use the same brake in the front with Ultegra, but I got rid of the travel agent. It's just not needed. Yes, it feels mushy when your stopped, but when riding they don't and you get superior braking and good modulation. You do need a straight wheel and the pads set close to the rim, but once it's set-up, it's as trouble free as any v.

I also use a canti in the rear, but I don't do loaded touring. It works ok, but they just don't brake as well as V's, but it's adequate for the rear in my case. I've had a V on the rear and it works fine (with Ultegra), but you definitely need a travel agent otherwise you get too much breaking; to hard to modulate the breaking force. I went to a canti only as an experiment as I don't care for messing with a travel agent although once set up they work fine.